Heretofore, as a means of distributing electric power to electronic units from a common on-vehicle power supply, electrical junction boxes are commonly known in which a power distribution circuit is constituted by a plurality of bus bars and a switch element and the like are incorporated into the power distribution circuit. An electrical junction box described in JP 2005-151624A (hereinafter referred to as Patent Document 1), for example, is known as this type of electrical junction box. A circuit assembly of this electrical junction box is configured so as to include a circuit unit, a heat radiation member having an adhesion surface to which the circuit unit is adhered, a case that houses the circuit unit, and a cover that is installed in an opening portion of the case.
If an electronic component is mounted on the circuit unit before the circuit unit is adhered to the heat radiation member, the circuit unit is likely to be deformed due to the thin plate shape thereof and the mount portion of the electronic component may be damaged by this deformation, and therefore care needs to be taken in handling the circuit unit in a period from when the electronic component is mounted until the circuit unit is adhered to the heat radiation member. In this regard, the electronic component can be mounted to a circuit unit that has already been adhered to the heat radiation member in the above circuit assembly, so that the circuit unit can be handled without needing such care as described above in a period from when the circuit unit is configured until the circuit unit is attached to the heat radiation member.
However, because the aforementioned circuit assembly is assumed to be attached to a heat radiation member, the problem cannot be resolved in a circuit assembly that does not include a heat radiation member. Also, because the circuit unit needs to be attached to a heat radiation member before an electronic component is mounted, the manufacturing method is restricted.